1/4 cup (4 tablespoons) unsalted butter
1 medium yellow onion, chopped
2 cloves garlic, cut small
1/4 cup all-purpose flour
1 1/2 cups milk
1 cup shredded cheddar cheese
1/2 teaspoon salt
3 pounds potatoes, peeled and cut into 1/8-inch-thick slices
1 tablespoon chopped fresh parsley (optional)
- Preheat oven to 350 degrees and grease a 9×13-inch baking dish with butter or baking spray.
- Melt butter in large saucepan over medium heat. Add onion and cook, stirring from time to time until soft, about 3 to 4 minutes. Add garlic and cook for about 30 seconds. Add flour and cook, stirring often until smooth, about 30 seconds.
- Slowly whisk in milk until fully mixed. Cook, stirring often until mix thickens, about 5 minutes. Remove from heat and whisk in cheese until smooth.
- Layer half of the potatoes in prepared baking dish. Spread half the cheese sauce over potatoes. Repeat with the rest of the potatoes and cheese sauce. Bake until potatoes are soft, and top is golden-brown, about 45 to 55 minutes. Top with parsley and serve.